There has been known rotation detector apparatuses and methods for detecting the number of rotations (rotation speed) and the amount of rotations of a rotating body with using a rotation detection signal outputted from sensors arranged along the rotational direction of the rotating body. Concretely speaking, there has been known a prior art rotation detector apparatus including a plurality of bridge-connected magneto-resistive effect elements arranged along the rotational direction of a rotating body such as a gear, and a binarization circuit for processing a detection signal, that receives a voltage value at a connection point of the magneto-resistive effect elements as a rotation detection signal, binarizes the rotation detection signal, and outputs a resultant signal. In addition, there has been known a prior art movement detector apparatus including a plurality of bridge-connected magneto-resistive effect elements arranged along the movement direction of a moving body such as a rail so as to detect the movement speed and the movement amount of the moving body, on which protruding portions and recess portions are alternately and repeatedly formed, and a binarization circuit for processing a detection signal, that receives a voltage value at a connection point between the magneto-resistive effect elements as a movement detection signal, binarizes the movement detection signal and outputs a resultant signal. Generally speaking, in the prior art rotation detector apparatus and movement detector apparatus, an analog sinusoidal detection signal corresponding to the teeth and valleys of the gear or the protruding portions and the recess portions of the rail is inputted to the binarization circuit. Therefore, by binarizing the detection signal into a binarized signal having a rectangular waveform using a predetermined threshold voltage, it is possible to detect the number of rotations and the amount of rotations of the rotating body or the movement speed and the movement amount of the moving body based on the time cycle and the number of pulses of the binarized signal.
However, since the magneto-resistive effect elements generally have thermal characteristics, the direct current level of the detection signal changes according to changes in the environmental temperature. For the above reasons, there has been such a problem that the detection signal cannot be binarized when, for example, the maximum value of the detection signal is smaller than the threshold voltage and when the minimum value of the detection signal is larger than the threshold voltage. Further, there has been such a problem that, if the above-described direct current level changes, the positions of the rising edges and the falling edges of the binarized signal change even when the detection signal can be binarized, and this leads to reduced edge accuracy. In order to solve such problems, the threshold voltage for binarization is adjusted based on the detection signal in the prior art apparatuses described in Patent Documents 1 to 3.
A data reproducing apparatus described in the Patent Document 1 includes means for reproducing and binarizing a reproduced signal read out from an information recording medium into digital data and means for demodulating the digital data. The data reproducing apparatus changes a predetermined constant of the digital data reproduction means based on a code error rate detected by the demodulating means, and adjusts the constant so that the code error rate becomes the minimum. In this case, the predetermined constant is a slice level of a level comparator for binarizing the reproduced signal with a predetermined level to perform an AND operation with a signal representing a zero-cross position of the signal obtained by differentiating the reproduced signal, and for generating a window pulse.
In addition, in a slice level adjustment circuit described in the Patent Document 2, it is paid attention that a “1” level and a “0” level exist at an even ratio in an EFM (Eight to Fourteen Modulation) signal produced with an accurate slice level, i.e., the average of the duty ratio is 50%. The slice level adjustment circuit automatically adjusts the slice level so that an average of a duty ratio of the EFM signal always becomes 50% by integrating the EFM signal in an integration circuit, comparing an integration output thereof with a reference voltage, and producing a control voltage to set the slice level of a waveform shaping circuit that produces the EFM signal from a high-frequency signal.
Further, a sensor signal processing apparatus described in the Patent Document 3 is characterized by including output correcting means which includes signal amplifying means, signal judging means, periodic signal generating means, counting means and output correcting means, peak and bottom holding means, threshold setting means, and comparing means. The signal amplifying means adds an offset signal to an output signal of a magnetism detection sensor, which detects magnetism, converts detected magnetism into an electric signal and outputs the electric signal as the output signal, and amplifies the output signal. The signal judging means outputs an offset adjustment start signal only when an output signal of the signal amplifying means exceeds a desired upper limit value or lower limit value. The periodic signal generating means outputs a periodic signal according to the offset adjustment start signal. The counting means changes a count value according to the periodic signal. The offset signal outputting means outputs an offset signal corresponding to the count value. The peak and bottom holding means holds a peak value and a bottom value of an output signal from the output correcting means. The threshold setting means sets a threshold value according to the peak value and the bottom value from the peak and bottom holding means. The comparing means compares an output signal from the output correcting means with the threshold value set by the threshold setting means, and outputs a binarized signal based a magnitude relation between the same signals.
The sensor signal processing apparatus described in the Patent Document 3 is configured to output the offset adjustment start signal to operate the periodic signal generating means only when the output signal of the signal amplifying means exceeds the desired upper limit value or the lower limit value. Therefore, when the output of the magnetism detection sensor changes and needs to be corrected, the output correcting means corrects the output of the magnetism detection sensor. If the output of the magnetism detection sensor is corrected so as not to exceed the desired upper limit value or the lower limit value, then the subsequent correcting operation is stopped. Namely, the periodic signal generating means to output the periodic signal for correcting the output is to be stopped. Then, since the periodic signal generating means to output the periodic signal for correcting the output is stopped at a timing at which the output signal from the output correcting means is compared with the threshold value set from the peak value and the bottom value by the peak and bottom holding means and the binarized signal is outputted, it is possible to prevent the degradation in the angular accuracy due to oscillation spike noises.